1. Field of the Invention
The present invention relates to a method for detecting an alignment mark for performing alignment, suitable for use in an exposure device or the like in producing semiconductor devices or the like.
2. Description of the Related Art
In producing semiconductor devices or the like, the most commonly used type of exposure devices utilize visible light or ultraviolet light in order to transfer a mask or reticle circuit pattern onto a wafer. With more advanced micromachining techniques of forming semiconductor circuit patterns, however, almost no further resolution can be provided, when visible or ultraviolet light is used to expose a pattern of the smallest size. Consequently, exposure using shorter wavelengths such as vacuum ultraviolet light or X-rays, or electron beams is drawing attention.
Putting such methods of exposure into practical use has the disadvantage that alignment of the mask and the wafer must be carried out with far greater precision than conventional alignments. In particular, when vacuum ultraviolet rays, X-rays, electron beams or the like are used, exposure must be carried out in a high vacuum, resulting in more severe conditions for alignment. At present, a method of exposure thought to be effective in detecting the position of an alignment mark is one using electron beams that provides high resolution. In general, however, multiple patterns are formed on the wafer by repeating the wafer forming process a plurality of times, causing the layer structure to change every time a cycle of the wafer forming process is repeated. Thus, an alignment mark, being detected using electron beams, is not necessarily detected under the same conditions, so that failure in the detection of an alignment mark may occur.